Titanium alloy valve based on composite ceramic coating and manufacturing process of titanium alloy valve

Abstract

The invention is applicable to the technical field of part surface strengthening, and provides a titanium alloy valve based on a composite ceramic coating and a manufacturing process thereof, the titanium alloy valve comprises a valve rod and a valve mounted at the bottom of the valve rod; an inserting part is arranged at the top of the valve, a valve rod inserting hole is formed in the bottom of the valve rod, the size of the inserting part is in interference fit with that of the valve rod inserting hole, and a composite ceramic coating is arranged on the valve. The process comprises the following steps of: firstly, performing laser texturing treatment on the surface of the air valve through laser texturing to form a laser textured layer and a micro-pit array structure; then, a NiCrAlY-TiN transition layer is sprayed through the HVOF spraying technology; and finally, a ZrO2-8Y2O3-5% SiC surface layer is sprayed through plasma spraying. Therefore, the high-temperature-resistant and wear-resistant performance of the valve rod can be remarkably improved, and the service life of the valve is prolonged.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of surface strengthening of parts, and provides a titanium alloy valve based on a composite ceramic coating and a manufacturing process thereof. BACKGROUND

[0002] Valves and valve stems are crucial components in internal combustion engines, primarily used to control the intake and exhaust of gases within the engine cylinders. Valves are responsible for controlling the intake and exhaust processes of the cylinders, ensuring the proper functioning of the engine. Valve stems are the core components of valves, supporting the opening and closing movements of the valves through their connection with valve seats. Valve stems often work in conjunction with other components of the valve to control the gases in the cylinders, ensuring the performance and efficiency of the engine under various operating conditions.

[0003] The structural design of valves and valve stems is typically cylindrical, with the length and diameter of the valve stem varying depending on the type and design requirements of the engine. Valve stems are usually made of high-strength alloy materials, requiring good mechanical properties, corrosion resistance, and high-temperature resistance. The manufacturing and processing of valves typically includes material selection, precision casting, machining, and heat treatment processes. The processing of valve stems includes turning, grinding, and heat treatment processes to ensure their precision and durability. During the manufacturing process, special attention must be paid to the hardness, surface finish, and wear resistance of the valve stem to ensure that it can withstand the use of the engine under harsh conditions such as high temperature, high pressure, and high speed.

[0004] However, in the working environment of high-pressure diesel engines, especially when the working temperature exceeds 800℃, the valve core will face extremely severe challenges. In high-temperature environments, the wear resistance of valve stems and their related components will significantly decrease, and problems such as high-temperature corrosion, oxidation, and wear will easily occur, thereby affecting the performance and service life of the engine. For example, traditional steel valve stems have a density of 7.8 g / cm 3 , resulting in excessive inertia force and limiting the increase of engine speed. Titanium-aluminum alloys and titanium alloys with a density of 4-4.43 g / cm 3 have superior performance, but their surface hardness is insufficient (HV330), and the friction coefficient with cast iron pipes (HV450-550) is as high as 0.35-0.45. To avoid the above-mentioned situations, existing coating technologies are usually used: PVD-TiN coating with a thickness of <5 μm, which significantly shortens the service life at high temperatures >400℃, and the coating effect gradually fails; or plasma spraying Al2O3 with a bonding strength of <50 MPa and poor thermal shock performance.

[0005] Therefore, the valve and the machining process of the valve in the prior art still have defects, and cannot meet the long-term stable working requirement of the high-pressure diesel engine under harsh conditions such as high temperature and high pressure, and a new technology capable of significantly improving the high-temperature and wear resistance of the valve rod is urgently needed to improve the service life of the valve. SUMMARY

[0006] In view of the above defects, the purpose of the present application is to provide a titanium alloy valve based on a composite ceramic coating and a manufacturing process thereof, aiming to solve the problems raised in the background art, including a valve rod and a valve installed at the bottom of the valve rod; the top of the valve is fixedly connected with a plug-in part, the bottom of the valve rod is provided with a valve rod insertion hole, the size of the plug-in part is matched with the valve rod insertion hole through interference fit, and the valve is provided with a composite ceramic coating.

[0007] Further, the plug-in part is a cylindrical structure; when the valve rod is heated, the inner diameter of the valve rod insertion hole at the bottom of the valve rod can allow the plug-in part to be inserted, and when the temperature returns to normal, the valve rod insertion hole and the plug-in part can be tightly matched as a whole.

[0008] Further, the bottom of the valve rod is provided with an embedded part, the embedded part is a frustoconical structure, the top of the frustoconical structure is integrally connected with the valve rod, the valve rod insertion hole is arranged at the bottom of the embedded part, and the top of the valve is provided with a valve embedded hole matched with the embedded part.

[0009] Further, the valve rod is provided with a valve rod screw hole, and the plug-in part is provided with a plug-in part screw hole corresponding to the valve rod screw hole.

[0010] A manufacturing process of a titanium alloy valve based on a composite ceramic coating, which processes and manufactures the titanium alloy valve based on the composite ceramic coating through the following steps, including:

[0011] First, the surface of the valve, including the head and the rod, is subjected to laser texturing treatment by laser texturing, to form a laser textured layer with roughness and a micro-pit array structure; then, a NiCrAlY-TiN transition layer is sprayed on the surface of the laser textured valve by using HVOF spraying technology; finally, the surface of the valve is subjected to plasma spraying of a ZrO2-8Y2O3-5%SiC surface layer.

[0012] Further, the valve and the valve rod close to the valve are subjected to machining pretreatment of the texturing layer by laser equipment, and the average roughness of the surface treated parts is controlled within the range of 5-10 μm.

[0013] Further, the top of the valve has a valve embedding hole, and the inner surface of the valve embedding hole is processed into a micro-pit array of a rough layer, the micro-pit diameter is 50-80 mu m, the depth-width ratio is 0.4, and the density is 150±20 pits / mm 2 .

[0014] Further, in the NiCrAlY-TiN transition layer coating step, 20% of titanium nitride nanoparticles with a size of 50-100 nm are added to the NiCrAlY material.

[0015] Further, in the ZrO2-8Y2O3-5% SiC surface layer, zirconium oxide, yttrium oxide and silicon carbide materials are used, and a transition metal boron-nitrogen ceramic is introduced into the ZrO2-8Y2O3-5% SiC surface layer.

[0016] Further, in the HfB2 and HfN powder pretreatment process, a high-energy ball mill under argon protection is used for mixing.

[0017] Therefore, the present application has the following beneficial effects:

[0018] 1. Bonding strength: The valve stem coating of the present application has a bonding strength of 85±3 MPa, which is much higher than the industry standard of ≥50 MPa (test method according to ASTM C633). Higher bonding strength means that the adhesion between the coating and the substrate is very strong, and it is not easy to appear peeling, falling off and other phenomena in the use process, which ensures the reliability of the valve stem in long-term operation. In the working environment of high-frequency vibration of the engine, the coating on the surface of the valve stem can still be firmly attached to the substrate, ensuring the normal opening and closing of the valve.

[0019] 2. High temperature wear resistance: The high temperature wear resistance test result of the present application is only 0.008 mm 3 / N·m, while the industry standard is 0.05 mm 3 / N·m (test method according to ISO7148-2018). Under high temperature conditions, the coating on the surface of the valve stem has excellent wear resistance, which can effectively reduce the material loss caused by friction and prolong the service life of the valve stem. In high temperature environment such as automobile engine, frequent friction between valve stem and valve seat will generate a lot of heat, and the coating of the present application can maintain good wear resistance at high temperature, reducing maintenance cost and replacement frequency.

[0020] 3. Thermal shock cycle: The coating of the present application can remain intact under frequent thermal shock conditions, and has excellent thermal stability, which is of great significance to ensure the safe operation of the engine. BRIEF DESCRIPTION OF DRAWINGS

[0021] Fig. 1Fig. 1 is a schematic view of a valve structure;

[0022] Fig. 2 Fig. 2 is a sectional view of the valve structure;

[0023] Fig. 3 Fig. 3 is a schematic view of a gas charging installation cavity structure;

[0024] In the drawings: 1-valve; 11-insert part; 111-insert part screw hole; 12-valve embedding hole; 2-valve rod; 201-valve rod screw hole; 202-stiffener; 21-valve rod insertion hole; 22-embedding part; 3-lower valve spring seat ring groove; 4-gas charging installation cavity; 41-inlet end; 42-outlet end; 5-heating coil; 6-clamping mechanism; 7-lifting platform; 71-valve tooling. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all of the embodiments of the present application.

[0026] It should be noted that in the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more; the terms "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", "third" and the like are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0027] Meanwhile, in the description of the present application, unless otherwise explicitly specified and limited, the terms "connected", "connected" should be broadly understood, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0028] In order to make the purpose, technical solutions and advantages of the present application more clear and explicit, the present application will be further described in detail below with reference to the drawings. It should be understood that the specific embodiments described here are only used to explain the present application, and are not used to limit the present application.

[0029] Reference is made to Figs. 1-3The titanium alloy valve based on the composite ceramic coating provided by the application comprises a valve stem 2 and a valve 1 installed at the bottom of the valve stem 2; the top of the valve 1 is fixedly connected with a plug-in part 11, the bottom of the valve stem 2 is provided with a valve stem insertion hole 21, and the size of the plug-in part 11 is matched with the valve stem insertion hole 21 through interference fit. The valve 1 is provided with a composite ceramic coating.

[0030] Specifically, the plug-in part 11 is in a cylindrical structure, at normal temperature, the outer diameter of the plug-in part 11 is slightly larger than the inner diameter of the valve stem insertion hole 21, and when the valve stem 2 is heated, the inner diameter of the valve stem insertion hole 21 at the bottom of the valve stem 2 can enable the plug-in part 11 to be inserted, and when the temperature returns to normal temperature, the valve stem insertion hole 21 and the plug-in part 11 can be tightly matched as a whole.

[0031] Preferably, the bottom of the valve stem 2 is provided with an embedded part 22, the embedded part 22 is in a frustum structure, the top (one end with a smaller diameter) of the frustum structure of the embedded part 22 is integrally connected with the valve stem 2, and at this time, the valve stem insertion hole 21 is arranged at the bottom of the embedded part 22. The top of the valve 1 is provided with a recessed valve embedding hole 12, the valve embedding hole 12 is matched with the embedded part 22, and when installed, the embedded part 22 can be inserted into the inside of the valve embedding hole 12, so that more stable connection and fixation are realized.

[0032] Preferably, the valve stem 2 is provided with a valve stem screw hole 201, the plug-in part 11 is provided with a plug-in part screw hole 111 corresponding to the valve stem screw hole 201, when the embedded part 22 can be inserted into the inside of the valve embedding hole 12, the two can be further fixed through a screw, so that further structural reinforcement is ensured.

[0033] Further, based on the structure of the titanium alloy valve based on the composite ceramic coating, the application further provides a manufacturing process of the titanium alloy valve based on the composite ceramic coating.

[0034] The manufacturing process provided by the application improves the performance of the titanium aluminum alloy and titanium alloy valve stem by adopting titanium aluminum alloy or titanium alloy as the base material of the valve stem, the preliminary processing flow of the base material, and the special material combination and the assembly processing of a plurality of parts after the post-processing.

[0035] For the manufacturing process of the titanium alloy valve based on the composite ceramic coating, the following processes are mainly involved, and the technologies of the processes are specifically described below to make the technical concept of the application clearer.

[0036] The present application carries out the processing pretreatment of the rough layer of the valve 1 and the end of the valve stem 2 close to the valve 1 (the outer surface of the embedded part 22 and) by the laser equipment. Specifically, the present process line utilizes the continuous wave laser system (IPGYLS-5000 fiber laser), preferably with the parameters of 400W power, 100ns pulse width and 20kHz frequency to process the alloy substrate surface; that is, the originally smooth surface is made rough by scanning the substrate surface with a high-energy laser beam, and a peak-valley microtexture is formed.

[0037] Specifically, the average roughness (Ra) of the part subjected to surface treatment is controlled within the range of 5-10μm. Thus, better "gripping points" are provided for the subsequent coating, and the adhesion of the coating to the substrate is enhanced.

[0038] Specifically, by parameter control of the laser equipment, the micro-pit array of the rough layer is formed on the other parts of the valve 1 except the outer surface of the embedded part 22, the micro-pit diameter is 50-80μm, the aspect ratio is 0.4, and the density reaches 150±20 pits / mm 2 The micro-pit array structure can ensure that the subsequent coating material can be filled into the inside of the micro-pit structure, improve the bonding strength, and the size and distribution of the micro-pit are optimized to minimize the mismatch of the thermal expansion coefficients d of the coating and the substrate. For example, the thermal expansion coefficients of TC4 and ZrO2 are different, and when they are combined together, they are prone to pulling or relaxation under the micro-mechanical structure, resulting in cracks and delamination between the coating and the substrate.

[0039] The present application adopts the NiCrAlY-20%TiN transition layer to coat the substrate. Specifically, NiCrAlY is a commonly used high-temperature alloy coating material, which has good high-temperature oxidation resistance and corrosion resistance. The present application adds 20% of TiN (titanium nitride) nanoparticles to the NiCrAlY material, and the size of the TiN nanoparticles is 50-100nm.

[0040] At the same time, the present application adopts high-velocity oxygen fuel spraying (HVOF spraying process), so that the TiN nanoparticles in the NiCrAlY substrate present a gradient distribution, that is, from the side close to the laser rough layer to the side close to the surface layer, the content of TiN gradually changes in a gradient distribution. It can alleviate the stress concentration problem caused by the difference in thermal expansion coefficients between different materials, realize smooth transition from the substrate to the surface layer, and avoid cracks or warping due to large material differences.

[0041] The present application adopts the ZrO2-8Y2O3-5%SiC surface layer to coat the bottom surface of the valve 1:

[0042] ZrO2-8Y2O3-5%SiC surface layer uses zirconium oxide (ZrO2), yttrium oxide (Y2O3) and silicon carbide (SiC) materials, which has excellent high temperature performance, heat insulation performance and wear resistance; the addition of 8% Y2O3 (yttrium oxide) in the ZrO2-8Y2O3-5% SiC surface layer can stabilize the phase structure of ZrO2, improve its high temperature stability and thermal stability. SiC has high hardness, high wear resistance and good corrosion resistance, and the addition of 5% SiC (silicon carbide) makes the entire surface layer have excellent heat insulation effect while enhancing its wear resistance and corrosion resistance.

[0043] Further, the ZrO2-8Y2O3-5% SiC surface layer used in the present application introduces transition metal boron-nitrogen ceramic cooperative phase (HfB2-HfN) in combination. Thus, the crack propagation is effectively prevented, the toughness is further improved, and the stress distribution is optimized.

[0044] The HfB2 and HfN introduced in the present scheme are both high melting point ceramics (>3300℃), however, HfB2 has a melting point of 3250℃ but poor oxidation resistance, HfN will oxidize above 1200℃, and the thermal expansion coefficients of both are about 30% higher than the matrix. The addition amount must be controlled below the percolation threshold, otherwise the coating will crack. The HfB2 / HfN addition amount proposed in the present application is ≤8wt%, and the SiC component is reduced to 4% to balance the total components.

[0045] For the powder pretreatment process of HfB2 and HfN, a high-energy ball mill under argon protection is used for mixing (the mixture contains YSZ, SiC, HfB2, HfN), and the ball milling time is ≤4h (to prevent grain coarsening). Thus, the ZrO2-8Y2O3-5% SiC surface layer used in the present application can provide wear resistance, ultra-high temperature strengthening and anti-creep properties, the hardness retention rate at 1100℃ is >80%, and the thermal shock life is increased by 60%. HfB2 and HfN doping can remain stable in harsh exhaust environments >1000℃, and can maintain stronger resistance to oxidation and molten salt corrosion when there are low-ash engine oil additives in the engine.

[0046] For HVOF spraying (high-velocity oxygen fuel spraying), the particle velocity is set to 750m / s. During HVOF spraying, the powder particles are accelerated to extremely high speed (750m / s) with an accuracy control of ±25m / s. High-speed particles impact the laser roughened substrate surface and quickly deposit to form a dense coating. High-speed impact helps to improve the bonding strength and density of the coating. Imagine a bullet flying at high speed hitting a wall, the bullet will be firmly embedded in the wall, and similarly, high-speed particles are more likely to be tightly bonded to the substrate.

[0047] Device parameter correspondence: Praxair JP-8000 device is adopted, kerosene flow is set to 25 L / min, and powder feeding rate is set to 35 g / min, so that the required particle velocity control is realized. Kerosene is used as fuel to provide energy, and the flow size affects the intensity and temperature of the flame, thereby affecting the acceleration and heating degree of the particles; the powder feeding rate determines the amount of powder entering the spray gun per unit time, and cooperates with the kerosene flow to make the powder particles obtain a suitable flight speed.

[0048] In the application, the valve 1 directly participates in the intake and exhaust process of the engine as a complete valve assembly, and needs to withstand high temperature, high pressure and frequent mechanical friction. Therefore, the valve 1 has very high requirements for the comprehensive performance of the coating, such as wear resistance, heat resistance and corrosion resistance. The valve stem 2 as a part of the valve assembly mainly plays a guiding and supporting role and will not directly contact high-temperature gas or withstand high-strength friction, so the requirements for some extreme performance are relatively low.

[0049] The application carries out a pretreatment process on the valve 1 and the valve stem 2 through different process steps, which specifically includes the following steps:

[0050] The valve 1 as a complete valve assembly applies the following process steps:

[0051] 1. Laser texturing: IPGYLS-5000 fiber laser is used to perform laser texturing treatment on the surface (including the head and stem) of the valve 1 at a power of 400 W, a pulse width of 100 ns and a frequency of 20 kHz, to form a laser textured layer with an average roughness (Ra) of 5-10 μm and a micropit array structure (diameter 50-80 μm, aspect ratio 0.4, density 150±20 pits / mm 2 ). The above steps provide a good bonding basis for the subsequent coating and ensure that the coating can be firmly attached to the surface of the valve 1.

[0052] 2. HVOF spraying: Praxair JP-8000 device is adopted, kerosene flow is set to 25 L / min, and powder feeding rate is set to 35 g / min, so that the powder particles impact the laser textured surface of the valve 1 at a speed of 750±25 m / s, and the NiCrAlY-20%TiN transition layer is sprayed. The transition layer has gradient distribution of TiN nanoparticles (50-100 nm), which can realize good matching with the substrate and the surface layer, alleviate the difference in thermal expansion coefficient and other problems, and improve the overall performance of the coating.

[0053] 3. Plasma Spraying: A ZrO2-8Y2O3-5% SiC topcoat is plasma sprayed onto the surface of valve 1. The coating's porosity is strictly controlled to below 1.5%, and online CT scanning monitors the porosity in real time to ensure the coating's density and quality. This topcoat provides valve 1 with excellent thermal insulation, wear resistance, and corrosion resistance, enabling it to better withstand harsh operating conditions such as high temperatures and wear.

[0054] As a component of the valve assembly, the valve stem 2 mainly connects the valve head and the valve drive mechanism. Compared with the valve 1, its working environment is relatively simple. It is mainly subjected to friction and wear along the stem and a certain degree of temperature change. The requirements for comprehensive performance such as heat insulation and wear resistance are relatively low. Therefore, some processes can be appropriately omitted. The specific processes are as follows:

[0055] 1. Laser texturing: Omit the laser texturing process of the valve embedded hole, and use laser texturing on other parts to increase the roughness of the valve surface and form a micro-pit array, which can improve the bonding strength between the coating and the rod substrate and prevent the coating from peeling off.

[0056] 2. HVOF Spraying: Omit the spraying of valve stem 2 and the valve insert on valve 1. Because valve stem 2 primarily bears the load, its requirements for high-temperature performance and comprehensive protection are not as stringent as those for valve 1. By omitting the HVOF spraying step, a relatively simple coating that meets the operational requirements of valve stem 2, such as a common wear-resistant coating, can be directly applied. This simplifies the process and reduces production costs without compromising the normal performance of valve stem 2.

[0057] Similarly, the valve holes do not need to be coated

[0058] 3. Plasma spraying: This step can be omitted. Valve stem 2 does not need to withstand the direct impact of high-temperature combustion gases and complex thermal stress variations that valve 1 does, so the thermal insulation requirements are less stringent. By omitting the plasma sprayed ZrO2-8Y2O3-5% SiC topcoat, not only process steps and costs are reduced, but also unnecessary performance redundancy that this coating may create on valve stem 2, while also not impacting its basic functionality.

[0059] In the above steps, the HVOF spraying step needs to be carried out under certain temperature conditions. When HVOF spraying is carried out under certain high temperature conditions, the surface temperature of the substrate material will increase appropriately, causing the sprayed particles to produce better plastic deformation at the moment of impact with the substrate surface. At the same time, due to the high temperature, the yield strength of the substrate surface material is reduced, making it more susceptible to deformation. Under such conditions, HVOF spraying can allow the high-speed impacting powder particles to be more deeply embedded in the micro-pits and rough textures on the substrate surface, forming a stronger mechanical bite, ensuring that the coating is not easy to peel off during subsequent use.

[0060] And for different material composition of the coating and substrate system, in its operation process, temperature change will cause thermal stress due to the difference in thermal expansion coefficient. But under high temperature conditions, HVOF spraying can make the coating gradually adapt to the thermal expansion state of the substrate during deposition, which helps to alleviate the thermal stress concentration between the coating and the substrate during operation. But in the existing valve 1 machining process, the valve 1 needs to be heated and sprayed before being installed with the valve stem 2, which will directly lead to more serious peeling between the coating and the substrate system due to the difference in thermal expansion coefficient, which will accelerate the damage of the valve 1.

[0061] Therefore, in addition to providing a HVOF spraying method by thermal spraying, the present application also provides an interference fit assembly equipment for the valve and a pre-process of thermal spraying.

[0062] The equipment includes a clamping mechanism 6 capable of clamping the upper end of the valve stem 2, a valve tool 71 capable of installing the valve 1, the valve tool is installed on the lifting platform 7, the lifting platform 7 is installed on the rotary table equipment, and the valve parts after machining can be driven to other processes. The equipment also includes an inflated installation cavity 4, and a heating coil 5 is installed inside the inflated installation cavity 4. The heating coil 5 uses electromagnetic induction heating principle; that is, when the bottom of the metal valve stem 2 extends into the alternating magnetic field of the heating coil 5, an induced electromotive force will be generated inside the metal, thereby forming eddy current, and a large amount of heat will be generated due to the resistance characteristics of the metal material, so that the end of the valve stem 2 is rapidly heated and deformed. At this time, the clamping mechanism 6 drives the valve stem 2 to descend, and the valve 1 is completed.

[0063] The inflated installation cavity 4 is provided with an air inlet end 41 and an air outlet end 42, and the air inlet end 41 and the air outlet end 42 are communicated with the external air pumping equipment, so as to exhaust the residual heat inside the continuously operating equipment.

[0064] Under the action of the heating coil 5, the heat will make the hole diameter of the valve stem insertion hole 21 increase, and the insertion process is completed. In the subsequent cooling process, the hole diameter is reduced to complete the interference fit. At the same time, due to the heat diffusion between the valve 1 and the valve stem 2, the outer surface of the valve 1 is further heated. At this time, the clamping mechanism 6 is released, the lifting platform 7 drives the valve tool 71 together with the valve stem 2 to descend, and enters the next HVOF spraying process. At this time, the valve 1 is heated due to heat diffusion, and the HVOF spraying process is directly carried out, which greatly improves the processing speed.

[0065] Of course, the present application can also have other various embodiments, and those skilled in the art can make various corresponding changes and modifications according to the present application without departing from the spirit and essence of the present application. However, these corresponding changes and modifications should all belong to the protection scope of the claims attached to the present application.

Claims

1. A titanium alloy valve based on composite ceramic coating, characterized in that: The invention comprises a valve stem (2) and a valve (1) mounted on the bottom of the valve stem (2); the top of the valve (1) is fixedly connected with a plug-in portion (11); the bottom of the valve stem (2) is provided with a valve stem insertion hole (21); the size of the plug-in portion (11) matches the valve stem insertion hole (21) through interference fit; and the valve (1) is provided with a composite ceramic coating.

2. The titanium alloy valve based on composite ceramic coating according to claim 1, characterized in that: The plug-in portion (11) is a cylindrical structure; when the valve stem (2) is heated, the inner diameter of the valve stem insertion hole (21) at the bottom thereof can allow the plug-in portion (11) to be inserted; when the temperature returns to normal temperature, the valve stem insertion hole (21) and the plug-in portion (11) can be tightly fitted into one body.

3. The titanium alloy valve based on composite ceramic coating according to claim 1, characterized in that: The bottom of the valve stem (2) is provided with an embedding portion (22), the embedding portion (22) is a frustum-shaped structure, the top of the frustum-shaped structure is integrally connected to the valve stem (2), the valve stem insertion hole (21) is provided at the bottom of the embedding portion (22), and the top of the valve (1) is provided with a valve embedding hole (12) matching the embedding portion (22).

4. The titanium alloy valve based on composite ceramic coating according to claim 1, characterized in that: The valve stem (2) is provided with a valve stem screw hole (201), and the plug-in portion (11) is provided with a plug-in portion screw hole (111) corresponding to the valve stem screw hole (201).

5. A titanium alloy valve manufacturing process based on composite ceramic coating, characterized in that: The titanium alloy valve based on the composite ceramic coating according to any one of claims 1 to 4 is processed and manufactured by the following steps, comprising: First, the surface of the valve (1), including the head and the stem, is laser-roughened to form a laser-roughened layer with a roughness and a micro-pit array structure; then, a NiCrAlY-TiN transition layer is sprayed on the laser-roughened surface of the valve (1) using HVOF spraying technology; finally, a ZrO2-8Y2O3-5% SiC surface layer is plasma-sprayed on the surface of the valve (1) by plasma spraying.

6. The titanium alloy valve manufacturing process based on composite ceramic coating according to claim 5 is characterized in that: The valve (1) and the valve stem (2) are subjected to a roughening layer pre-processing process at one end close to the valve (1) using laser equipment, and the average roughness of the surface-treated parts is controlled within the range of 5-10 μm.

7. The titanium alloy valve manufacturing process based on composite ceramic coating according to claim 5 is characterized in that: The top of the valve (1) is provided with a valve embedding hole (12). Except for the inner surface of the valve embedding hole (12), other parts of the valve (1) are processed into a micro-pit array of a roughened layer, with a diameter of 50-80 μm, a depth-to-width ratio of 0.4, and a density of 150±20 pits / mm 2 .

8. The titanium alloy valve manufacturing process based on composite ceramic coating according to claim 5 is characterized in that: In the NiCrAlY-TiN transition layer coating step, 20% of titanium nitride nanoparticles are added to the NiCrAlY material, and the size of the titanium nitride nanoparticles is 50-100 nm.

9. The titanium alloy valve manufacturing process based on composite ceramic coating according to claim 5, characterized in that: The ZrO2-8Y2O3-5%SiC surface layer adopts zirconium oxide, yttrium oxide and silicon carbide materials, and the ZrO2-8Y2O3-5%SiC surface layer adopts a composite transition metal boron-nitrogen ceramic synergistic phase.

10. The titanium alloy valve manufacturing process based on composite ceramic coating according to claim 9, characterized in that: The powder pretreatment process of HfB2 and HfN is to mix them in a high-energy ball mill under argon protection.

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